Category: air defense

Shortly after 1440 on 15 September 1942, in the waters of the Solomon Islands, USS Wasp (CV-7) was struck by three torpedoes from the IJN submarine I-19. The impact point was directly below the AVGAS distribution station, which was in operation when the torpedoes struck. Within minutes, Wasp was engulfed in flames, roaring like a furnace, punctuated by powerful explosions from built-up gasoline vapors. Ammunition and aerial bombs began to detonate from the heat, and inside of an hour, Captain Forrest Sherman ordered Wasp abandoned. She burned well into the evening before torpedoes from USS Lansdowne (DD-486) finally sank her.

When I was a young lad, I read an excellent book on the Solomons Campaign. In it, the author described Wasp as burning like a torch, and how, as darkness fell, sailors on other ships could see her glowing red from the fires inside. When Wasp finally slipped beneath the waves, it was said she emanated a loud and eerie hissing as her hot steel sank into the sea. Watching the footage above, one understands that such a description, like Tom Lea’s famous painting, is hardly hyperbole.

In all, 193 sailors died on Wasp, and 366 were wounded. Forty-three precious aircraft also went down with her. She had been in commission just 28 months.

In the 37 weeks of war since December 7th, the US Navy had lost Langley (CV-1), Lexington (CV-2), Yorktown (CV-5), and Wasp (CV-7). Also soon to be lost was Hornet (CV-8), sunk at Santa Cruz on 26 October 1942. Hornet, however, would be the last US fleet carrier lost during the war.

Just over fifty years ago, the USAF flew a mission for the first time dedicated to suppressing SA-2 Surface to Air Missile sites in North Vietnam. In spite of the US Army having widely deployed a very similar system domestically for years, the Air Force knew little about the best way to accomplish the mission, which came to be known as Wild Weasel, or more properly, Suppression of Enemy Air Defenses, or SEAD. Tactics, techniques and procedures (TTP) would emerge along with new weapons and technology.

The first dedicated weapon for this SEAD mission was the AGM-45 Shrike, a missile derived from the AIM-7 Sparrow with a passive seeker that homed in on the electromagnetic power radiated by a radar set. Hence the term Anti-Radiation Missile, or ARM.

The Shrike had a few issues, however. Most critically, it had a shorter range than the SA-2 it was intended to counter. But it also had another glaring weakness. If the radar it was attacking suddenly stopped transmitting, it had no means to guide to the target, and would miss.

Still, the mission was suppression of enemy air defenses. By forcing radar operators to shut down, even for a short while, that allowed the main strike package to transit and strike its primary target.

Unfortunately, that simply meant the same suppression would have to be undertaken day after day. The later AGM-78 Standard ARM and its replacement, the AGM-88 High Speed ARM, or HARM, attempted to avoid the shutdown defense by integrating a strapdown Inertial Navigation System (INS) that would guide the missile to the last known position of the emitter. Unfortunately, many modern SAM radars, particularly short range systems, and extremely mobile. Nor were early INS systems particularly accurate. The shutdown still meant most radar systems survived attack.

[youtube https://www.youtube.com/watch?v=WUWLajfDOPg]

The frustration of having to repeatedly spend sorties, time, and ordnance on enemy air defenses lead to something of a doctrinal shift, particularly after Desert Storm and the 1999 air campaign over Kosovo. Emphasis shifted from suppression to Destruction of Enemy Air Defenses, or DEAD (usually pronounced “dee-ad” as opposed to “dehd”). While jamming and HARM would be used to suppress radar guided SAMs, the attack would be pressed and launchers, radars, control sites and communications nodes would be attacked with either conventional munitions, or guided weapons such as Laser Guided Bombs (LGBs), the GPS guided Joint Direct Attack Munition (JDAM) or the gliding GPS guided Joint Stand Off Weapon (JSOW).

The improvements in guidance technologies led the US Navy to reexamine the state of the art in ARMs.This became the Advanced Anti Radiation Guided Missile program, or AARGM. Money for an entirely new ARM wasn’t available, but some funds were, so research began. What they found was that the basic HARM motor and airframe were generally acceptable. The improvements in technology, however, meant that a far more capable seeker system was possible.

What resulted was the AGM-88E HARM. Externally virtually indistinguishable from its predecessors, the AGM-88E uses a much improved passive radar seeker. It also uses a datalink receiver known as Intergrated Broadcast System- Receiver (IBS-R) to receive positional data on threat emitters gathered by Electronic Intelligence (ELINT) platforms such as the EP-3E and RC-135. It also uses a GPS updated INS platform for better guidance. Finally, it has a millimeter wavelength active radar seeker for terminal guidance.

[youtube https://www.youtube.com/watch?v=FCBs1IEk9Fc]

[youtube https://www.youtube.com/watch?v=Id8DEiaKgvQ]

AARGM is in service with the US Navy and Marines. And having just entered service in 2012, the Navy is now looking at a further upgrade, with an RFI issued recently seeking to increase the missile range, most likely through an improved solid rocket motor. What is interesting is that the RFI also lists as a threshold capability internal carriage on the F-35A/C (due to the lift fan, the F-35B has a slightly different internal weapons bay layout).

On Saturday, May 23, a visiting family made a most unusual discovery at Manassas Battlefield. They found what appeared to be an unexploded 20th century shell while out hiking and brought it to the Visitor Center. Park law enforcement staff called in the state police bomb squad and subsequently evacuated the Visitor Center and Henry Hill. The bomb squad later confirmed the shell was inert and harmless.

First and foremost, if you find anything that even remotely resembles unexploded ordnance, do not touch it. Note the location and inform the authorities.

As it turns out, the EOD detachment was able to discern the projectile was a T-231 rocket. Which got me digging, what the heck is a T-231? Well, it was a 2.75 inch diameter (70mm) rocket projectile, sometimes referred to as HEAA.

Forgive us for not having a lot of concrete information on this, but it appears that not more than a relative handful were constructed. We infer that HEAA stands for High Explosive Anti-Aircraft. That is, in spite of the notation in the Facebook post that it was an air to air weapon, it was in fact intended as the ammunition for a ground based anti-aircraft gun system. What’s that, you say? How does a rocket work in an anti-aircraft gun? Well…

One of the challenges in anti-aircraft gun fire control is the lengthy time of flight for the shells to reach the target area. The longer the time of flight, the greater the chance the target will maneuver away from the aimpoint selected as much as an entire minute before. Remember, while a projectile fired from a cannon might have great velocity as it leaves the muzzle, it immediately begins to decelerate due to both gravity and air resistance. Thus, the closer to maximum effective range, the slower and slower the shell is moving.

If there were a way to have the velocity of the projectile remain constant over the course of its time of flight, or even just significant portion, that would simplify the fire control problem. A rocket, of course, accelerates as long as its motor continues to burn, until it reaches its maximum possible aerodynamic speed. Rockets of those days were, however, somewhat inaccurate weapons.

And so it appears the Army tried an intriguing approach to combining both a gun and a rocket into one weapon. The T-231 was packed inside a recoilless rifle shell casing. That is, it had an open end and was fired from a recoilless rifle. The firing charge imparted a relatively modest muzzle velocity of about 1000 feet per second to the round. The initial charge also served to ignite the round’s rocket motor, which then boosted it to a velocity of about 3000 feet per second, roughly on par with the muzzle velocity of existing anti-aircraft guns. But the small size of the projectile meant there was a correspondingly small rocket motor (and less size for a warhead as well) and that limited the burn time for the motor.

The program never really went beyond a handful of test firings, mostly to gather data. The performance wasn’t significantly better than existing anti-aircraft artillery, and the first generation of guided missiles was just reaching operational status at the time, rendering the project obsolete.

Craig did point out one mystery yet to be solved. The test firings apparently took place at Wallops Island. So how did the projectile find its way to Manassas? We may never know.

In the early 1950s, the Air Force closely monitored the introduction of surface to air guided missiles (SAM) such as the Nike Ajax into service with the Army Anti-Aircraft Command. Under joint operating doctrine for continental air defense at the time, SAMs were the Army’s responsibility, with fighter interceptors an Air Force role. The Air Force was interested in a very long range SAM system, however, and adopted the quaint stance that such a SAM was simply an unmanned interceptor.

Building on earlier work with GAPA, Boeing was teamed with the Michigan Aerospace Research Center (MARC) to develop a long range pilotless interceptor. Between BOeing and MARC, the project was quickly dubbed BOMARC.

Two major challenges for a long range SAM were propulsion and guidance. Rocketry was still rather primitive, and a rocket motor simply couldn’t provide the range needed. A gas turbine couldn’t provide enough thrust for high speed except at great expense. Boeing instead proposed using the simple Marquardt ramjet to give the missile a speed of about Mach 2.8 and a range of about 200 miles. Ramjets are simple and work very well at high speed, but they cannot provide thrust at zero airspeed, so a booster rocket was needed to accelerate the missile off the launch pad. Solid motors were considered, but a sufficiently powerful one wasn’t available, so a liquid fueled rocket was built into the after end of the airframe.

Even at M2.8, at would take a BOMARC some time to reach its 200 mile range, and so a mid-course guidance was needed to keep the missile on track to intercept. Here is where Boeing and MARC came up with a pretty elegant solution. Air Defense Command was already using the SAGE network to provide steering commands to manned interceptors. BOMARC would simply use that system to provide steering commands to the missile autopilot. Terminal guidance would be an onboard active radar pulse doppler seeker.

The warhead was either a 1000 pound conventional warhead, or a 10 kiloton W40 nuclear warhead.

The missiles would be stored horizontally in semi-protected bunkers nicknamed coffins, and raised to vertical for launch. The liquid fueled rocket had to be fueled immediately before launch, which was both somewhat dangerous, and took a few minutes, which, if a real intercept was at hand, was an obvious drawback.

The Air Force had originally planned 52 launch sites with 120 missiles each. In the event, costs of the system, budget cuts, and developmental problems led to the deployment being scaled back to a handful of sites in the US and Canada, with a total of about 570 operational missiles being built, with maybe another 100 development and service test missiles also built.

Even before the BOMARC was deployed, Boeing and Morton Thiokol worked on developing a sufficiently powerful solid booster. After about 290 “A” model BOMARCs had been delivered, production switched to the “B” model with the XM51 solid booster. As an added bonus, the XM51 took up much less space in the airframe. That extra space was used for more fuel (the ramjet ran on 80 octane gasoline), giving the “B” model more than double the range, over four hundred miles.

With this much improved missile entering service, the earlier A models were soon converted to high speed drone targets.

BOMARC served from 1959 to 1972. As the threat of intercontinental ballistic missiles increased, the BOMARC became increasingly irrelevant, and a costly white elephant. It was the only surface to air missile system the Air Force ever developed.

[youtube https://www.youtube.com/watch?v=4duys7RhTvo]

A bit on designations- BOMARC was, as noted, concieved as a pilotless interceptor, and thus was initially numbered under the fighter designation system as F-99. The Air Force soon changed its designation system for guided missiles and changed the designation to IM-99 (intercept missile). Under the revised 1962 Tri-Service Designation system, the BOMARC became the CIM-10.

When we discussed the DEW Line in our series on Continental Air Defense, we briefly mentioned the less than wholly successful Texas Towers, early warning radars on the eastern seaboard mounted atop platforms similar to oil drilling rigs in the Gulf of Mexico. Here’s an interesting look at the fabrication and emplacement of the first of the Texas Towers.

Some of the most interesting curiosities in the history of naval warfare surround older warships remaining in service long after similar vessels have been retired. Sometimes, the story of such ships is one of tragedy, like the three elderly Royal Navy cruisers sunk in the Channel by a German U-Boat in 1914, or the nearly-helpless Spanish wooden-hulled Castilla, quickly sunk at Manila Bay. Other times, like with Oldendorf’s “Old Ladies” at Surigao Straits or the Iowas in Desert Storm, the veteran ships were found to still be plenty lethal. One such curiosity is the unlikely tale of USS Allen, DD-66.

The rapid advances in Naval technology that spanned the last decade of the 19th Century and the first decade of the 20th included generational leaps in warship design, hastened further by the outbreak of war in 1914. Nowhere was this more manifest than in the smallest of the combatant ships of the world’s navies, the destroyer. Originally the “torpedo boat destroyer” built to protect larger ships of the battle line from the speedy small craft and their ship-killing weapons, powered torpedoes, soon these “torpedo boat destroyers” became the carriers of torpedoes themselves, then called simply, “destroyers”.

US destroyer construction in the early part of the century followed apace with designs elsewhere. Small, largely coastal craft evolved into the 700-ton “flivvers” and later, the “thousand-tonners” of the O’Brien, Tucker, and Sampson classes. Despite being almost new, these 26 ships of the latter three classes had proven barely suitable for the requirements of destroyer service in a modern war at sea. Among the first US ships to attach to the Royal Navy in 1917, by the end of the war they were hopelessly outdated, as the British W and V classes, and the latest German destroyers, were significantly larger, much faster, far more capable warships.

Following the Armistice, almost all the “thousand tonners” were quickly decommissioned, as they were replaced in service with the “flush-decker” Wickes and Clemson classes, of which an astounding 267 were built (though few were completed in time for war service). A number of the obsolescent “thousand tonners” were given to the US Coast Guard, where they served into the 1930s. Most, however, were scrapped or sunk as targets. Most, but not all.

One unit of the Sampsons, USS Allen, DD-66, was placed back in commission, to serve as a training ship for US Navy Reserve personnel. She would serve in this role between 1925 and 1928, after which she returned to the Reserve Fleet in Philadelphia. Allen was retained even while a number of her younger and far more capable “flush-decker” sisters were scrapped. As war clouds loomed, Allen was selected to be recommissioned, in the summer of 1940. She must have been an exceptionally well-maintained vessel. Even with that, the choice to recommission Allen was a curious one. She and her sisters were designed before the First World War, and still reflected the “torpedo boat destroyer” mission in her layout and systems.

After some time in the Atlantic, Allen was assigned to the Pacific Fleet, which had recently moved to Pearl Harbor. She was present and fired her only shots of the war during the attack on Pearl Harbor on 7 December 1941. Lacking adequate endurance and weapons, Allen spent the war escorting vessels between the Hawaiian Islands, helping to train submarine crews by acting as a mock sub chaser, and she made the occasional voyage back to the US West Coast. In the course of the war, Allen had her antiaircraft armament considerably augmented, with six 20mm cannon, and she lost at least one set of torpedo tubes. She gained depth charge throwers, and even a modest air search radar. I could find no reference to her being fitted with sonar of any kind, however. (And if Norman Friedman didn’t say it happened, it didn’t happen!)

Immediately following the war, of course, the worn-out and thoroughly obsolete Allen was quickly decommissioned, in the fall of 1945, and just as quickly sold for scrap. She is shown above, disarmed and awaiting disposal. At the time of her decommissioning, she was the oldest US destroyer in commission, and the last survivor of her class and type. Built to specifications which dated to before US entry into the First World War, USS Allen would serve through the Second, a throwback of four generations of destroyer design. A remarkable record of service indeed.

Recent news that Russian leader Vladimir Putin will deliver S-300 missiles to Iran has raised concerns that the US, Israel or other nations would lose any ability to use military force to delay, degrade or eliminate Iran’s pursuit of a nuclear weapons program. Setting aside the political aspects for a moment, let us take a look at the dreaded S-300 Surface to Air Missile System (SAM).

The Russians have had a robust SAM development program just as long as the United States, and arguably had better results than the US. The Russian S-25 (NATO reporting name SA-1) Berkut and S-75 (SA-2) Dvina SAMs were roughly analogous to the US Nike Ajax, and the S-125 (SA-3) Neva was analogous the US HAWK missile. Similarly, the S-200 (SA-5) Angara fulfilled a role much as the US Nike Hercules.

A historical aside- the Soviet Union had two distinct air defense organizations. The first V-PVO, the Soviet Air Defense Forces, was a separate military service dedicated to the air defense of the Soviet Union, with its own interceptors and surface to air missile systems, and associated warning and control systems. The second was The Air Defense of Ground Troops, which was similar in mission to our own US Army Air Defense Artillery. Obviously the needs of the two forces were quite different, and so each service tended to pursue different missile systems.

That’s important, because when we talk about the S-300 SAM system, it’s important to realize that there are two entirely distinct families of S-300 with vastly different capabilities. The S-300V family is a national defense asset. The system that Iran has purchased, and which Moscow seems ready to deliver, is the S-300P family, originally designed to protect Soviet forces in the field.

Watching US forces in Vietnam, and Israeli forces in the Yom Kippur war learn to negate the early generation Soviet SAMs through jamming and Wild Weasel tactics, the Soviet Union began development of what would become the S-300 families. Prime objectives were better mobility for the system, to allow “shoot and scoot” capability, longer missile range, better kinematics (energy and maneuverability) for the missile, greater rate of fire, increased resistance to jamming and other ECM, and reduced vulnerability to anti-radiation missiles that homed in on the SAM battery radar.

When the Soviet Union began developing the next generation of SAMS in the 1970s, several related areas were seeing significant advancements in the state of the art, such as integrated circuits and solid state electronics, reliable digital computers for signal processing and data management, improvements in solid rocket motors, and a shift from mechanically scanned radars to phased arrays.

Let’s talk about the organization of SAM units. The basic unit is the battery, which is a roughly company sized organization, and is the smallest unit capable of independently completing an engagement. That is, it has the resources to acquire, track, identify, and engage a target. This in effect means that each battery has a command post, an acquisition (or search) radar, an engagement radar, and one or more Transporter, Erector, Launch (TEL) vehicles which hold the actual SAMs themselves. Typically, a battery would have three TELs, each with four launch tubes, for twelve missiles. Usually two missiles are tasked to each target, so a battery can normally engage six targets before it needs to reload. Typically, two to five batteries are integrated into a battalion to cover an even wider area.

The S-300P, manufactured by Almaz, was first fielded in the late 1970s and known in the West as the SA-10 Grumble. As noted, a battery consisted of a command post, an acquisition radar, and engagement radar, and usually three TELs.

Each of the four elements is integrated to the S-300P system, but over time, each of the four elements was also upgraded, or even replaced to enhance the capability of the system. For instance, the original engagement radar, the Flap Lid (5N63), has given way to the Tomb Stone* (30N6) radar. Improvements in one element improve the overall system. And over the course of the life of the S-300P, pretty much every element has been upgraded or replaced by an improved system, to such effect that modern S-300P systems are in effect completely different systems from the original, though care has been taken to ensure backward compatibility.

Iran originally ordered S-300P in for delivery in 2008, but UN imposed sanctions, while not explicitly barring delivery, have to this point led Russia to hold off from closing the deal. Reportedly, the Iranians will receive the S-300PMU1, also known as the SA-20A Gargoyle A.

Let’s take a look at the elements of the SA-20A.

[youtube https://www.youtube.com/watch?v=4YGaq8QW0x4]

The command post is the 54K6E.

Note the antenna for data link connection to the radars and TELs of the battery, though it can also be connected via cable.

While the system sold to Iran is reportedly the SA-20A, exactly which radars associated with the sale are included are something of a mystery. And the Russians have a vast array of, well, arrays available to chose from. One high end system is the 64N6E Big Bird.

The Big Bird is a large passively scanned phased array. In fact, the array is larger than the arrays of an Aegis radar on a US destroyer. Normally the Big Bird scans in azimuth by mechanically rotating the array, and scans in elevation by electronic beam steering. It can stop the rotation, and scan a sector of 60~90 degrees azimuth by electronic beam steering. Detection range against high flying fighter sized targets is credited as being around 150 miles. Of course, due to the earth’s curvature and the resulting radar horizon, detection range versus low altitude targets is much shorter. Consequently, many S-300P systems also use a dedicated radar for low altitude search. The radar horizon issue persists, but the radar is optimized for operating in the ground clutter environment. One such radar is the 76N6E Clam Shell.

Rather than emitting one beam and rotating to move the beam, a phased array uses thousands of phase shifters mounted in an array (hence the name) to electronically steer the main search beam, and can also simultaneously transmit and receive secondary beams. For instance, it might be searching its engagement sector, while simultaneously also tracking half a dozen targets for engagement. It is also frequency agile, so the targets being tracked don’t receive a continuous stream of energy at the same frequency, making it harder for the target to realize it is under attack, and further, making it much more difficult to jam.

The SA-20A missile itself is the 48N6, a large, single stage missile quite similar to our own early Patriot missile. The SA-20A is cold launched vertically from a four tube launcher mounted either on a truck or semi trailer.

It is generally credited with an effective range of anywhere from 40 to 80 miles versus an aerial target. It has a maximum speed of about Mach 6, though the average speed, particularly for longer range engagements, is more typically around Mach 2 or Mach 2.5. In addition to engaging aircraft and cruise missiles, it has a limited capability against short ranged ballistic missile type targets.

The SA-20A uses a guidance technique known as Track Via Missile, or TVM. There are a couple different variations on TVM, but most work generally the same. Let’s walk through a hypothetical engagement to show how TVM works.

The Big Ben acquisition radar detects a target in the battery’s sector.

The target is displayed on the command posts scopes.

The command post initiates the engagement by queuing the Tomb Stone engagement radar to lock onto the target.

The Command post tasks a TEL to engage, and gives the 48N6 missile’s autopilot initial steering commands to follow.

The missile launches vertically, then tips over to the direction of the estimated intercept point.

As the missile flies toward the target, the Tomb Stone uses a radar beam to illuminate the target.

A passive radar receiver in the missile receives the reflected radar energy from the target, and transmits that information in a coded stream back to the Tomb Stone radar.

The Tomb Stone radar sends that message to the command post.

Fire direction computers in the command post generate steering commands for the missile, and transmit them to the Tomb Stone radar.

While still illuminating the target, the Tomb Stone radar also sends the coded steering commands to the missile, which generally has a receiver antenna in the back of the missile’s fins.

The missile corrects its flight path.

Note that as the missile gets closer to the target, it is receiving ever more of the reflected radar energy from the target. In essence, it gets more accurate as it gets closer. TVM means that the illumination beam doesn’t need to be as powerful as a conventional semi-active homing system. Further, the missile can be somewhat cheaper, as the computing power is not on board the missile, but in the command post.

[youtube https://www.youtube.com/watch?v=Hl8btwQ-X2k]

[youtube https://www.youtube.com/watch?v=QtuN8UuAWTg]

Cold Launch doesn’t always work as planned.

While the SA-20A has a formidable low altitude capability, it is optimized for the mid to high altitude counter-air role.** Since the US has, since the end of the Vietnam War, tended to operate at those altitudes to avoid low technology defenses such as gunfire and short range IR guided missiles, that poses a challenge for the US and other nations with a similar operational philosophy.

That the S-300P is a formidable air defense system is without question. But can we (or more likely, the Israelis, or less likely, the Saudis) penetrate to a target defended by it.

Well, yes, but…

As we’ve seen in air campaigns from the 1982 Israeli-Syria Bekka Valley war through Desert Storm, and Allied Force in Kosovo, the first phase of a campaign is to disintegrate the enemy Integrated Air Defense System. Some of that can be as simple as putting a Tomahawk cruise missile in the headquarter of the enemy’s air defense organization. Other weapons used to suppress or destroy air defense assets can include the Army’s ATACMs short range ballistic guided missile system. The problem is that precise targeting is needed to attack a system such as the S-300P. The S-300P can be moved in as little as five minutes. So the targeting has to be in virtually real time. To do that requires an investment in quite a few electronic warfare aircraft or other system. Once found, simply attacking it is a challenge. The maximum range of the SA-20A is nominally greater than the range of the HARM anti-radar missile normally used to attack SAM systems.

But the US, and its allies, tend to eschew taking a system versus system approach, and instead use multiple avenues to address any single platform. For instance, attacking any target protected by an S-300P would almost certainly involve significant numbers of electronic warfare aircraft, such as the EA-18G Growler, both for locating the SAM site, and for jamming the associated radars, as well as launching HARMs at them. Other supporting HARM shooters would also be used.

A promotional video explaining how multiple weapons can be used to overwhelm advanced SAM defenses:

[youtube https://www.youtube.com/watch?v=5Pu_PKpEhqU]

Bottom line, while the S-300P system in Iran would not preclude the US or its allies penetrating defended airspace, it would make such a task much more difficult, and likely time consuming. It would also greatly increase the risk of crew losses or captured airmen.

Having said that, if the alternative is a nuclear armed Iran, it seems that risking treasure and lives is worth it.

* Current Russian designation systems are somewhat impenetrable to my mind, so I’ve tended to mostly use the NATO Reporting Name for a given system.

**It is also quite typical for an SA-20A battery to have a modern short range air defense system such as the Tor-M1 (SA-15 Gauntlet) co-located for terminal defense of the battery itself.